1. Field of the Invention
This invention generally relates to laser scanning systems for reading bar code symbols and, more particularly, to scan pattern generators for generating scan patterns with changeable scan directions which extend across the symbols to be read.
2. Description of the Related Art
Laser scanning systems and components of the type exemplified by U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,593,186; 4,496,831; 4,409,470; 4,460,120; 4,607,156; 4,673,805; 4,736,095; 4,758,717; 4,760,248; 4,806,742; 4,808,804; 4,825,057; 4,816,661; 4,816,660; 4,845,350; 4,835,374; 4,871,904; 4,896,026; as well as U.S. application Ser. Nos. 193,265 now U.S. Pat. No. 5,144,120 --all of said patents and patent application being owned by the assignee of the, instant invention and being incorporated as specified below by reference herein--have generally been designed to read bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working or reading distance from a hand-held or stationary scanner, and with a reading spot of a certain size, the spot being scanned over each symbol to trace a scan line.
It has previously been proposed to generate scan patterns of mutually parallel scan lines extending along one or two directions, as well as omni-directional scan patters of intersecting scan lines, and even curvilinear scan patterns, for superposition over the symbol to be read to insure that, no matter what the angular orientation of a respective symbol might be within predetermined limits, at least one of the scan lines or part of the pattern will be scanned over the entire length of the respective symbol. Yet, the known patterns are generated by highly complex and expensive systems.
Also, quite apart from the angular orientation of the symbols to be read, one symbol might be located close-in to the scanner, whereas another symbol might be located far-out from the scanner and, in short, successive symbols may be located at different working distances from the scanner. In the case of a scanner which has been designed to read symbols within a certain range of working distances, should it occur that a particular symbol falls outside this range, then the distance between the scanner and the symbol must be adjusted, and usually within a short time interval, for, otherwise, the symbol will not be read. In the case of a hand-held scanner, the scanner is usually manually moved toward or away from the symbol to adjust the distance between the scanner and the symbol. This can be a tiring procedure and require multiple reading attempts. It would be desirable, therefore, if the scan pattern generators also incorporated a so-called "zoom" characteristic in which the working distance is automatically changed during scanning.
It would further be desirable to change the scan pattern to further insure that at least one of the scan lines, or part of the pattern, will scan the entire length of the symbol to be read. Some symbols may be more rapidly or successfully decoded and read by a particular scan pattern.
In the same vein, changing the scan rate from a slow to a faster speed, or vice versa, might spell the difference between a successful and a non-successful decoding and reading of a particular symbol.
In order to minimize power consumption, which is of especial concern in a hand-held scanner having an on-board battery, it would be desirable to vary the intensity of the light beam emitted by a light source, typically a laser, mounted within the scanner For example, the light source, rather than, for instance, being shut down when a symbol is not being read, may be underpowered to generate a low power laser beam which would be useful during aiming. Thereupon, during reading, the laser may be powered up to generate a high power laser beam.